The physiological perception of three-dimensional information by the human brain is a complex phenomenon. Generally, numerous inputs are received by the human brain and integrated with logical operations and experience to generate the perception of a picture of the outside world in three dimensions.
One way of presenting three-dimensional information to a viewer is to simulate binocular vision and provide a pair of pictures with a variation of the perceived scene corresponding to changes in point of view. Because the right and left eyes both see a given scene from different points in space, the positions of various objects with respect to each other in the images created by the lenses of the left and right eyes on their respective retinae are different, and the scene is perceived in three dimensions.
This may be understood if one considers two spherical objects of equal size positioned in space along a line which also includes the left eye of a viewer. The left eye of the viewer will see only the object (the "first object") which is nearer to it.
On the other hand, if the other spherical object is sufficiently distant from the first spherical object, it will be completely visible to the right eye of the viewer. In contrast, if the objects are somewhat closer together, part of the other object will be occulted by the nearer object. If the other object is positioned closer and closer to the nearer object, progressively more of the other object may be occulted until, depending upon the size of the objects relative to the distance from the viewer and the interocular separation, only a sliver of the other spherical object will be visible. Thus, each of the eyes produces and sends to the brain a different picture of the outside world.
Experience is used by the brain to evaluate the relative positions of elements on the basis of the images produced by the right and left eyes. By evaluating such things as the amount of an object that is visible, relative perceived object positions and perceived object sizes, three-dimensional information can be reconstructed with the resultant perception of a three-dimensional scene.
Thus, one way of producing a three-dimensional effect is to photograph a scene using two cameras separated by from 60 to 75 mm, a distance roughly corresponding to the average human interocular distance, that is the distance between the human eyes. Just as each human eye would view the scene at a slightly different point of view relative to the other eye, each camera in this system photographs the scene from a slightly different point of view relative to the other camera to generate right and left images.
To achieve separation, the images may be colored so that one image will have substantially one color, for example red, while the other image will have substantially another color, for example green. The right and left images may then be projected and seen only by the right and left eyes of the viewer, respectively, through the use of a pair of eyeglasses with red and green lenses.
When a viewer wearing these glasses views the scene produced as above, the green lens of the glasses will filter out and prevent the viewer's right eye from seeing the image of the scene that is green, and the red lens will filter out and prevent the viewer's left eye from seeing the image of the scene that is red. Thus, each eye observes the scene from the point of view it would in the real world and the brain interprets the scene as three dimensional.
These glasses have lenses that are colored to correspond to the color of one of the images. In particular, if the image taken with the right camera is substantially red, the lens in the glasses that is in front of the viewer's left eye is red, If the image taken with the left camera is substantially green, the lens in the glasses that is in front of the viewer's right eye is green. Colors may be selected to give some perception of full color.
If a true full-color three-dimensional display is desired, the two images produced by the two cameras may be positioned on a single frame of film such that the image from one camera is positioned directly above the image from the second camera.
To view the scene, the full-color images would be projected, for example, onto a movie screen. The image on the top corresponding to the image taken by one of the cameras and the image on the bottom corresponding to the image taken by the other camera are projected by a projection system which projects the corresponding right and left images so that they are substantially superimposed with respect to each other on the screen. However, the light from the top image is filtered to have a polarization orientation which is perpendicular to the light of the bottom image.
To see the desired three-dimensional effect, a viewer must wear special glasses with a pair of polarizing filters which each match a respective one of the polarizations of the light from the top and bottom recorded images.
Thus, with polarized lens glasses, each eye would look through a lens polarized at a 90.degree. angle from the lens for the other eye and each eye perceives only one of the stereoscopic images.
A great disadvantage with these systems for projection of three-dimensional scenes is the necessity of the use of special glasses. The viewer must wear the special glasses in order to perceive the three-dimensional effect.